A field of use for such glass panes is the production of solar modules. Solar modules are composed, as a rule, of a photosensitive semiconductor layer provided with a transparent covering for protection against external influences. For this purpose, the individual solar cell units are mostly laminated between a glass pane and a flexurally resistant rear cover pane, for example made from glass, with the aid of an adhesive film or an adhesive. The transparent adhesive must surround solar cell units completely, be UV-stable and be completely bubble-free after the laminating process.
Since the solar cell units are extremely sensitive to breaking, curing casting resins or cross-linkable ethylenevinylacetate (EVA)-based systems are often used as transparent adhesive. In the uncured state, these adhesive systems can be adjusted to have such low viscosity that they surround the solar cell units in a bubble-free manner. After the addition of a hardener or cross-linking agent, a mechanically resistant adhesive layer is obtained. The disadvantage of such solar modules is that they are complicated to produce. Particularly in the case of large-surface facade elements, the embedding of the solar cell units into the liquid casting resin and the controlled curing of the latter constitute a process which is difficult to control. Moreover, some casting resins tend after a few years to form bubbles or to delaminate.
DE 199 50 893 C2 describes a solar module with marginal sealing. The object on which this solar module is based is to specify an even further-improved sealing off of a thin-layer structural element by means of a chalcopyrite absorber layer, as compared with the prior art. Such a chalcopyrite absorber layer serves, in conjunction with a desiccant, to enable moisture to be absorbed and to provide a climate-stable encapsulation of solar modules.
In a solar module with thin-layer solar cells arranged between two panes and sealed by means of a casting compound, with marginal sealing arranged at the outer margin of the panes and composed of a spacer and of at least one adhesive strand applied in portions to the latter on the outside, and with solar cell terminals led outward from the space surrounded by the panes, this object is achieved in the following way. The spacer is composed of an elastomer strand provided with a moisture-absorbing agent, the adhesive strand continuously surrounding the elastomer strand on the outside.
However, this method is suitable only for the production of relatively small solar modules.
DE 101 22 437 A1 discloses a hot-melt adhesive in the form of a granulate, and in view of the prior art given there the set object of the inventors is here to provide single-component moisture-reactive hot-melt adhesive compositions which can be produced and can be applied in free-flowing or pourable form.
This publication describes, further, a method for connecting sheet-like structures or moldings, which is characterized by the following method steps:
a) homogenizing and melting of the reactive granulate powder, if appropriate in an inert atmosphere, with the exclusion of moisture and/or oxygen, using a heatable mixing assembly, if appropriate with high shearing,
b) extrusion of the homogenized reactive thermoplastic mixture, if appropriate by means of a shaping nozzle, onto at least one surface of a sheet-like structure or molding;
c) joining of a second sheet-like structure or molding, matching this, to the applied layer of reactive mixture,
d) if appropriate, mechanical fixing of the joined sheet-like structures or moldings,
e) cooling of the composite system thus formed to room temperature, the reactive hot-melt adhesive composition solidifying and curing along with cross-linking.
The structures or moldings which are under consideration here are wooden or furniture parts, textiles and vehicle parts, but also solar collectors. However, indications as to the special requirements, such as arise in the case of the bubble-free bonding of large-surface glass panes, cannot be found here.
A photovoltaic concentrator module with a multifunction frame is known from DE 10 2006 007 472 A1. The basic object is in this case to provide a photovoltaic concentrator module which can be produced cost-effectively, has a long service life and makes it possible to integrate simply and flexibly additional components which cannot be accommodated or can be accommodated only with difficulty on the lens plate or bottom plate. Furthermore, a method is supposed to be developed which makes it possible to produce such concentrator modules. This method is characterized in that a frame (3), connecting a lens plate (1) and a bottom plate (2), is arranged along the margin of the lens plate (1) and bottom plate (2), and in that, between the frame (3) and the lens plate (1) and/or the frame (3) and the bottom plate (2), on the one hand, at least one first sealing compound (4) and/or adhesive compound (4) and, on the other hand, at least one second sealing compound (5) are introduced along the frame (3) peripherally over at least part of its length, the two sealing and/or adhesive compounds differing from one another in their curing times and/or gas permeabilities. Here, too, two plates are connected to one another, but any indication as to the special problems in the connection of large-surface glass panes cannot be found.
An alternative to curing adhesive systems is the use of films based on polyvinylbutyral (PVB). Here, the solar cell units are embedded between PVB films, and these are connected under increased pressure and increased temperature to the desired covering materials to form a laminate. In this method, the projecting film also has to be removed after pressing and heating. For this purpose, a device for trimming photovoltaic modules is known from DE 20 2008 008 794 U1.
Furthermore, an adhesive for the production of composite glass is known from DE 198 36 695 A1, the use of this adhesive in a method for the production of composite glass free of marginal sealing being described. The object on which this publication is based is to provide, for the production of composite glass, an adhesive which bonds in the finished composite glass between the glass panes, instead of a casting resin, has high viscosity and makes it possible to use a novel automated method for the production of composite glass free of marginal sealing.
The method, described in DE 198 36 695 A1, for using this adhesive in a method for producing composite glass has the following steps:
a) the glass panes are cleaned and dried,
b) the adhesive is applied to the inside of the first glass pane lying horizontally,
c) the second glass pane is laid congruently onto the adhesive layer,
d) the sandwich arrangement obtained is pressed and the adhesive layer is cured by
UV radiation.
Examples given for the formats of the composite glasses produced in this way amount to a maximum of 1500×1000 mm. These, however, are not large-surface glass panes within the meaning of the invention. Moreover, the composite glasses described have obviously been manufactured merely in individual pieces.